<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
	</head>
	<body>
		<script type="text/javascript">
			document.getElementById("upload_file").onchange = function () {
				gen_base64();
			};
			function $_(id) {
					return document.getElementById(id);
			}
			function gen_base64() {
				var file = $_('upload_file').files[0];
				r = new FileReader();  //本地预览
				r.onload = function(){
					$_('base64_output').value = r.result;
				}
				r.readAsDataURL(file);    //Base64
			}
		</script>
	</body>
</html>